Polymer, positive resist composition, and patterning process

Abstract

A positive resist composition comprising a polymer comprising recurring units of a specific structure adapted to generate an acid upon exposure to high-energy radiation, recurring units of a lactone ring-containing structure, and acid labile units, all the recurring units being free of hydroxyl, can form a fine size pattern having a rectangular profile and improved collapse resistance.

1 . A polymer comprising
 recurring units of a structure adapted to generate an acid in response to high-energy radiation selected from UV, deep UV, electron beam, x-ray, excimer laser, γ-ray and synchrotron radiation, having the general formula (1a) and/or (1b),   recurring units of a lactone ring-containing structure having the general formula (2a) and/or (2b), and   acid labile units having the general formula (3),   all the recurring units being free of hydroxyl,   
       
         
           
           
               
               
           
         
       
       wherein R 1  is hydrogen or methyl, R 2  is hydrogen or trifluoromethyl, R 2 , R 4 , and R 5  are each independently a substituted or unsubstituted, straight, branched or cyclic C 1 -C 10  alkyl, alkenyl or oxoalkyl group, or substituted or unsubstituted C 6 -C 18  aryl, aralkyl or aryloxoalkyl group, any two of R 3 , R 4 , and R 5  may bond together to form a ring with the sulfur atom, R 6  and R 7  are each independently a substituted or unsubstituted C 6 -C 18  aryl group, 
       
         
           
           
               
               
           
         
       
       wherein R 1  is hydrogen or methyl, 
       
         
           
           
               
               
           
         
       
       wherein R 1  is hydrogen or methyl, x is 0 or 1, and L is an acid labile group. 
     
     
         2 . A positive resist composition comprising the polymer of  claim 1  as a base resin. 
     
     
         3 . A pattern forming process comprising the steps of coating the positive resist composition of  claim 2  onto a substrate and heat treating to form a resist film, exposing the resist film to high-energy radiation, and developing with a developer. 
     
     
         4 . The process of  claim 3  wherein the high-energy radiation has a wavelength in the range of 180 to 250 nm. 
     
     
         5 . The process of  claim 3  wherein the exposing step is to expose the resist film to high-energy radiation via a liquid according to the immersion lithography. 
     
     
         6 . The process of  claim 5 , further comprising the step of forming a protective film on the resist film,
 the exposing step of immersion lithography including interposing a liquid between the protective film and a projection lens.   
     
     
         7 . The process of  claim 6  wherein the high-energy radiation has a wavelength in the range of 180 to 250 nm. 
     
     
         8 . The process of  claim 7  wherein the liquid is water.